The present invention relates to equipment for automatic following-up of tools, in particular welding torches, along the boundary lines of the workpieces and/or the edges of the workpieces, with a magnetic scanning device, which works without contact, but is connected to the tool. Such equipment is applied in particular, when workpieces are butt-welded together by the autogenic-protective-gas-, or plasma-welding process. When butt-welding, the workpieces can be in contact or slightly spaced, depending upon which seam preparation is provided such as the case of an I-, I-, V-, X-, Y- or K-shaped seam preparation. Such seam preparations do not all allow a follow up of the welding burner by either mechanical scanning of the seam, or by photoelectrical processes.
The deficiencies of such scanning processes is caused, on the one hand, by the small distance between the plates, as mentioned above. On the other hand, the photoelectric scanning processes fail, because the optical contrast between the gap, which is formed between the two workpieces, and the metal areas limiting this gap, are too small.
Further difficulties for following up by the mechanical scanning, result also, because as often results in practice, the edges of the workpieces to be welded together are mechanically unsymmetrically treated at the preparation of the edges, or due to the fact that the plate-thickness fluctuates, that the plates are not level, or that the scanning mechanism finds insufficient guidance, due to the preceding root- and/or tackweldings.
To avoid the above-mentioned disadvantages of mechanical or photoelectric scanning devices, for the welding gap, it is known from German Patent DL-PS 55096, to scan the edges to be welded together, by means of a magnetic scanning device. For this purpose, only one scanning head is provided which scans the magentic stray-field, which leaves the area to be welded (hereinafter designated as gap). The outlet signal of the scanning head is led in as a lateral, regulating signal of a device for the lateral adjustment of the welding burner. However, such a device has the disadvantage that only ferro-magnetic materials can be scanned. A further disadvantage is that because of the scanning oscillation which is led back and forth with a definite frequency over the gap, only a gap larger than 0.5 mm. can be scanned. Beyond that, such a device is not suited to scan workpieces which are already connected in the root area of a welding seam - the gap being already closed by a lowest root layer.